The intensity of the scattered radiation is proportional to its frequency to the fourth power, so blue light is scattered much more strongly than red light.the longer-wavelength light is more transmitted while the shorter-wavelength light is more reflected via scattering. For larger particles, scattering increases in the forward direction and decreases in the backwards direction as the result of constructive and destructive interference .
If a beam of light is passed through a turbid sample, its intensity is reduced by scattering, and the quantity of light scattered is dependent upon the concentration and size distribution of the particles. In nephelometry the intensity of the scattered light is measured, while, in turbidimetry, the intensity of light transmitted through the sample is measured.
Nephelometry and turbidimetry, both techniques are like colorimetry.
Both technique are scattering of light by on non transparent particles in suspended in a solution.
Turbidimetry is the process of measuring the loss of intensity of transmitted light due to the scattering effect of particles suspended in it. Light is passed through a filter creating a light of known wavelength which is then passed through a cuvette containing a solution. A photoelectric cell collects the light which passes through the cuvette. A measurement is then given for the amount of absorbed light.
Turbidimetry can be used in biology to find the number of cells in a solution.
In turbidimetry, the measured transmittance, T, is the
ratio of the intensity of source radiation transmitted by the sample, IT, to the intensity of source radiation transmitted
by a blank, I0.
T=IT/I0
The relationship between transmittance and the
concentration of the scattering particles is similar to that given by Beer’s
law:
–logT=kbC(10.32)
where
C is the
concentration of the scattering particles in mass per unit volume (w/v),
b is the
pathlength, and
k is a
constant that depends on several factors, including the size and shape of the
scattering particles and the wavelength of the source radiation.
Nephelometry: an instrument for studying the
density of suspended particles in a liquid by measuring the degree to which the
suspension scatters light.
Nephelometry is a technique used
in immunology to determine the levels of several blood plasma proteins. For
example the total levels of antibodies isotypes or classes: Immunoglobuli M, Immunoglobulin
G, and Immunoglobulin A. It is important in quantification of free light chains
in diseases such as multiple myeloma.
This technique is widely used in
clinical laboratories because it is relatively easily automated. It is based on
the principle that a dilute suspension of small particles will scatter light passed through it rather than simply absorbing
it. The amount of scatter is determined by collecting the light at an angle.
In nephelometry the relationship between the
intensity of scattered radiation, IS, and the concentration
of scattering particles is
|
|
IS = kSI0C
|
where
I0 intensity
of incident light
kS is an empirical constant .
Is
is the source radiation’s intensity.
C is the
concentration of the scattering particles
kS is determined from a calibration curve
prepared using a series of standards containing known concentrations of analyte.
Application :
Purity of waterDetermination of inorganic substance
Biochemical analysis
Quantitative analysis
Determination of CO2
